The present invention relates generally to neural electrodes, and in particular to a neural electrode that will remain stable in its position in the spinal canal.
Epidural electrical stimulation in the spinal cord has been shown to be effective in relieving certain types of intractable pain so that many patients can drastically reduce or even eliminate the use of pain relieving drugs when epidural stimulation is used as part of a pain treatment program. One approach to providing such electrical stimulation is to introduce an electrode into the epidural space overlying the spinal cord.
When this method is used, obtaining proper location of the electrode is usually critical. In the demyelinated, sclerosed spinal cord (as in Multiple Sclerosis), for example, there are a limited number of responsive regions along the length of the spinal cord to which the electrode should be applied. And present surgical procedures require a mid-line placement, not only to ensure that both sides of the body receive the benefits of the stimulation but also to prevent painful stimulation of the lateral margins of the spinal cord where the sensory spinal roots are found.
Generally the electrode is at the tip of a lead inserted into the spinal cord through a Touhy needle. A problem that typically occurs after placement of the lead is that of general migration. Not only does the electrode tip tend to move laterally from the ideal mid-line position (there being, in general little to prevent this) but there have been many instances of axial retraction of the tip due to tensile forces on the lead itself. This latter problem seems to accompany major activity of the back muscles, as occurs, for example, when one does push-ups.
The major contribution to the problem of electrode stability is the relatively long length of lead between the electrode tip and the site of exit from the spinal canal (some 15 to 20 cm away) where the lead is, or should be, anchored with a suture or a suturable silicone rubber clamp. The tendency of a helical lead structure, which is usually used in these procedures, is to lay straight, which is an advantageous attribute. However, this characteristic can work against the surgeon who leaves a subcutaneous loop of lead material just outside the spine such as for strain relief. The stress this creates in the loop of helical wire, which prefers a straightened configuration, places a small but constant tension upon that portion of the lead in the spinal canal, and will dislodge it unless special anchoring techniques are employed. The major problem facing any proposals for firm electrode anchoring technique relates to spinal cord sensitivity. Virtually any nontrivial forces placed upon the cord can do it permanent damage.
Accordingly it is an object of the invention to provide a neural electrode lead that will maintain its position in the spinal canal after it is inserted. It is another object to provide such a lead that will avoid injurious contact with the spinal cord. It is still another object to provide such a lead that can be used with existing tools and techniques for the insertion of leads into the spinal canal.
Further objects of the invention are to provide an effective neural electrode that is stabilized and directional in place, that is simple and economical to manufacture, and that may be easily used by medical personnel. Other objects and features of the invention will in part be apparent and in part be pointed out hereinafter.